Lake Jordan was a prehistoric glacial lake in Montana that formed during the late Pleistocene, in the closing stages of the late Wisconsin glaciation. As the Laurentide Ice Sheet advanced south from central Alberta, the Havre lobe blocked regional drainage systems, including the ancestral Missouri River, allowing meltwater to collect between the ice margin and the Rocky Mountains. Part of a chain of temporary proglacial lakes across the northern Great Plains, Lake Jordan later drained eastward toward the Yellowstone River and Glacial Lake Glendive. Deposits near Great Falls help reconstruct this Ice Age episode and show how glaciers reshaped Montana’s river systems.